The former US Open champion had broken 70 only once in his previous 20 rounds on the European Tour this year, and despite a bogey-bogey finish, McDowell is seeing light at the end of a dark tunnel.

He was joined in a group on 66 - four-under par - by Shane Lowry, with Thorbjorn Olesen of Denmark the overnight leader after a superb 63.

Next best was England's Danny Brooks (64) followed by a cohort on 65 which included American Jimmy Walker and former Irish Open champion Richard Finch.

This was a day of high-octane scoring on the Gullane course which, for this tournament, is a composite layout consisting of 16 holes of Gullane No 1 and two holes from the No 2 course at the venue.

The morning players had the better of the conditions as the wind strengthened to between 20-25 kph in the afternoon.

McDowell had six birdies on his card, including four in a row from holes five through eight after 16 holes.

He was disappointed with a lip-out putt on the par-3 17th for a bogey four, and another bogey on 18, but overall his mood was positive going into today's round.

"Yeah, it's always disappointing to finish with a couple bogeys but there was some good stuff today.

"I drove the ball really well. Some nice iron play. The putter was pretty hot sort of the first 11 or 12 holes and cooled off a little coming in but the greens were perfect out there today, really, really great scoring conditions this morning. I'd have taken that going out, and I'll take it now," he said.

Shane Lowry, by contrast, is high on confidence.

With a little luck, he could have got more out of his round.

Against that, his overall play was solid and his lag putting from distance helped save par on a number of occasions.

Scoring

"It's a decent score and gives me a good chance going into tomorrow and into the weekend," he said.

"I'm just happy with the good start. It felt like it could have been a couple better, but I'll take that."

Lowry's blemish-free round featured birdies at holes one, three, ten and the par-5 16th with some narrow misses on at least four more holes.

"That got me going for the back nine. It's a very fair golf course. If you play good golf, you shoot a good score.

"If you hit bad shots there's a lot of bunkers out there off the tee that can penalise you.

"I managed to stay out of the bunkers today and hopefully I can stay out of them for the rest of the week," he said.

Pádraig Harrington, winner of the Honda Classic on the PGA Tour last March, shot a two-under 68.

Damien McGrane was on one-under, Michael Hoey on level-par, and Paul McGinley left himself a mountain to climb after an opening 76. The leaderboard was awash with red numbers which makes for a fascinating race to improve today and, for those in the lower placings, to make the cut.

Last year's winner Justin Rose made plenty of birdie chances but had to settle for a 66 as did American pair Matt Kuchar and Rickie Fowler.

Phil Mickelson, who won the Scottish Open and the Open Championship in successive weeks in 2013, was on one-under par after a 69.